1. Field of the Invention
The present invention relates to a typewriting apparatus, and more particularly to a typewriting apparatus in which a carrier is driven by a stepping motor.
2. Related Background Art
In ordinary typewriters, the stepping motor for driving a carrier at printing operation is driven always with a constant control pulse rate (a constant timing of energizations of driving phases of the stepping motor) both for frequently used letters and symbols (for example, a, b, c, . . . , A, B, C, . . .) and for letters and symbols which are not frequently used but require higher positional precision (.vertline., .sub.-- etc. which show evident defects in printing such as broken or staggered line if the positional precision is not high enough), and no particular control for each letter or symbol has been made.
In the conventional typewriting apparatus, because of the above-explained reason, it has been necessary to employ such driving system and driving pulse rate that will provide sufficient precision of printing position for the above-mentioned symbols such as .vertline. and .sub.--, so that the driving system has been inevitably expensive. On the other hand, in order to reduce the cost of the driving system, ball bearings in the carrier driving system etc. are recently often replaced by sliding bearings, and such change inevitably increases hysteresis or backlash in positioning of the carrier driving system, thus significantly deteriorating the precision of printing position. In order to prevent such hysteresis or backlash, it has been proposed to regulate the pulse rate when the carrier is stopped by the stepping motor. In such method, however, since the driving system is so controlled as to push the play or backlash of the system always to one direction, the approach to a desired position has to be made slowly in order to prevent vibration at stopping, so that the control inevitably requires a longer time. Therefore, such control method, if employed in the printing of all the letters and symbols, significantly reduces the printing speed though it provides a higher precision of printing position.